The invention relates generally to gas absorbers, and more particularly to a temperature-based method and system for estimating the remaining absorptive capacity in a gas absorber such as a CO2 absorber used in a re-breathing apparatus.
Closed circuit re-breathing systems are used by underwater divers, miners, firefighters, hazardous material handlers, and a variety of other personnel that must work in environmental conditions where breathable air is either unavailable or in short supply. In general, a re-breather includes a carbon dioxide (CO2) absorber or scrubber in its exhaust gas breathing loop. The CO2 absorber includes material that will xe2x80x9cabsorbxe2x80x9d (i.e., react with) the CO2 in the exhaust gas. Since the removal of CO2 is critical, it is important for the user to know when the CO2 absorber is losing its ability to absorb exhaled CO2.
To address this problem, a variety of approaches have been used. For example, U.S. Pat. No. 4,154,586 discloses a method in which the CO2 absorbent material changes color when it is spent. However, in underwater diving and fire fighting applications, the user may not be able to see such a color change. Another approach is described in U.S. Pat. No. 4,146,887 where a temperature difference between the ambient environment and one location inside the absorber is measured and used to provide an xe2x80x9cend-of-lifexe2x80x9d indication. Still another approach is described in U.S. Pat. No. 4,440,162 where temperature is measured at a predetermined location in the absorber. When the temperature exceeds a pre-set value, an alarm is triggered. However, variations in ambient conditions can cause an end-of-life indication or an alarm to come too early or too late in the life of the absorber.
Since the endurance of a CO2 absorber varies with ambient temperature/pressure and with a user""s breathing rates, it is desirable to provide a user with ongoing information as to the remaining capacity of the CO2 absorber. However, the above-described prior art approaches are either impractical for certain applications or do not provide such ongoing information.
Accordingly, it is an object of the present invention to provide a method of estimating the remaining absorptive capacity of a gas absorber.
Another object of the present invention is to provide a method and system of providing a visual display of the remaining absorptive capacity of a gas absorber that absorbs a gas during an exothermic reaction.
Still another object of the present invention is to provide a method of estimating the remaining absorptive capacity of a CO2 absorber.
A still further object of the present invention is to provide a method of estimating the remaining absorptive capacity of a gas absorber of a CO2 absorber in a way that is nearly independent of ambient conditions.
Yet another object of the present invention is to provide a method of visually displaying the approximate remaining absorptive capacity of the CO2 absorber used in a re-breathing system.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, a method and system are provided for estimating remaining absorptive capacity of a gas absorber that absorbs a gas (e.g., CO2) during an exothermic or endothermic reaction therewith. The gas absorber is disposed in a flow of the gas such that the gas flows into an inlet of the gas absorber and flows therethrough along a flow path. Inside the gas absorber, a reaction gas is produced by the exothermic or endothermic reaction and exits the gas absorber at an outlet thereof. A plurality of temperature sensors are distributed along the flow path. The temperature sensors include a first temperature sensor positioned at the gas absorber""s inlet and subsequent temperature sensors spaced apart along the flow path. Temperatures at each temperature sensor are measured and temperature differences between each subsequent temperature sensor and the first temperature sensor are determined. Each temperature difference is normalized using the largest of the temperature differences so that corresponding normalized temperature differences are generated. The normalized temperature differences are indicative of the remaining absorptive capacity of the gas absorber. More specifically, processing includes the selection of a calibration function that is based on an experimentally-determined relationship between the normalized temperature differences and the remaining absorptive capacity. The remaining absorptive capacity can be represented visually on a display as a percentage of an initial absorptive capacity of the gas absorber or as a function of the amount of the gas (that is to be absorbed) that exits the outlet of the gas absorber.